Needs for flat panel display to be used for a display of a computer has been increased accompanied with spreading of information terminals. Moreover, chances of providing information by electronics media are increased, which have been provided hitherto by paper media, accompanied with progress of the information systems, and needs for electronic paper or digital paper to be used as thin and easily portable mobile displaying media have also been increased.
In the flat panel displays, the displaying media have been generally formed by using an element such as a liquid crystal, an organic EL or an element utilizing electrophoresis. In such a displaying media, technology using an active type driving element (TFT element) as the image driving element forms main stream for holding the brightness uniformity of the image and the image rewriting rate. For example, the TFT elements are formed on a glass substrate and sealed together with liquid crystals and organic EL elements in usual computer displays.
In such the case, semiconductors such as a-silicon (amorphous silicon) and p-Si (polysilicon) can be used. The TFT element can be produced by forming a source, drain and gate electrodes on a substrate by forming piled layers of such the silicon semiconductors and a metal layer according to necessity. A vacuum production process such as spattering apparatus is usually necessary for producing such the TFT element.
For producing such the TFT element, the vacuum production processing using a vacuum chamber should be repeated several times for forming each of the layers so that the costs for the equipment and running thereof become enormous. For example, repeating for several times of processes such as spattering, CVD, photo-lithographing, etching and washing is necessary in usual for producing the TFT element, and the element is formed on the substrate through several tens processes. In such the production method using the Si semiconductor, a considerable design change in the production equipment such as the vacuum chamber is necessary for responding to the requirement for large size display so that the change in the equipment can not be easily performed.
Moreover, the material of the substrate is limited to one capable of withstanding to the temperature in the process since a process to be carried out at high temperature is included in the usual TFT producing processes using the Si material. Therefore, glass should be actually used for the substrate. When the thin type display such as the electronic paper or the digital paper is constituted by such the usual TFT elements, the display becomes heavy and loses softness resulting in becoming breakable by the shock of falling. Such the properties caused by producing the TFT elements on the glass plate is not desirable for satisfying the needs of the easily portable thin display accompanied with the progress of the information system.
On the other hand, investigation on organic semiconductor materials having high electric charge transportat ability is aggressively progressed in recent years. Such the compound is expected to apply, for example, for organic laser oscillation element such as that discussed in Non-patent Document 1, and organic thin film transistor reported in Non-patent Document 2 and other reports, additionally to the electric charge transportation material for organic EL elements. When such the organic devices are realized, it is considered that the production process can be simplified by applying vapor deposition at relatively low temperature under vacuum or low pressure and a soluble semiconductor material can be produced by suitably modifying the molecular structure. Furthermore, production of the organic element by printing method including an ink-jet method becomes possible if the organic semiconductor solution can be prepared. Though it has been considered hitherto that such the production process at low temperature can not be applied for usual Si type semiconductor material, there is possibility of that the process can be applied to the device using the organic semiconductor material. Consequently, the limitation relating to the heat resistivity of the substrate is alleviated so that the TFT element can be formed on a transparent resin plate. If the TFT element can be formed on the transparent resin plate and a displaying material can be driven by the TFT element, a display having lighter weight and higher flexibility than those of the usual display and is hardly or very difficultly broken by falling may be obtained.
The organic semiconductor materials investigated for realizing such the TFT element have been limited to: an acene such as pentacene and tetracene (cf. Patent Document 1, for example); a phthalocyanine including lead phthalocyanine; a low molecular weight compound such as perylene and a tetracarboxylic acid derivative thereof (cf. Patent Document 2, for example); an aromatic oligomer typically a thiophene heximer such as α-thienyl and sexithiophene (cf. Patent Document 3, for example); and a conjugate polymer such as polythiophene, polythienylenevinylene and poly-p-phenylenevinylene (cf. Non-patent Documents 1 to 4). Therefore, development of a semiconductor composition using a new charge transfer material showing high carrier mobility has been desired.
In Japanese Patent Publication Open to Public Inspection (hereafter referred to as JP-A) No. 2003-292588, U. S. Patent Opened Application Nos. 2003/136,958, 2003/160,230 and 2003/164,495, described are that “When a polymer TFT is used as the logical element of integrated circuit to be used for microelectronics, the mechanical durability is largely improved and the life timed thereof is prolonged. However, it is considered that many semiconductive polythiophenes are instable when they are in contact with air since such the compounds are each oxidized by doping by atmospheric oxygen so that the electric conductivity is increased. As a result of that, the off-current in the device prepared from such the material is increased and the ON/OFF ration of the electric current is reduced. Therefore, it is necessary for many of these compounds to pay sever attention for preventing or minimizing the oxidation doping by removing oxygen in the environment in the course of the processing of the material and the device production. Attraction of the polymer TFT as the economical technology, specifically for large screen displays, for replacing the silicon TFT technology is reduced since such the preventing measure results in a higher cost. The above-mentioned and other shortcomings can be avoided or minimized in the embodiments of the invention. Accordingly, an electronic device having high resistivity against oxygen and relatively high ON/OFF current ratio is demanded.” and proposed is a countermeasure for solving the problems. However, the level of the improvement has been insufficient and further improvement has been desired.
Furthermore, it has been disclosed that an electroconductive compound having repeating units each having a structure in which a 5-member ring including a sulfur atom is contained can be applied for the above objects (cf. Patent Document 4, for example). However, concrete example of the 5-member ring include sulfur atom other than thiophene ring is not disclosed and there is no description suggesting other structures. Consequently, the properties of the compounds of the present invention having a thiazole moiety when the compounds are applied for the above-described objects have been difficult. Though Patent Document 5 discloses organic semiconductor materials each having a thiazole ring, any compound having a partially connected thiazole structure is not described and the description regarding the molecular weight of the compound is unclear, and there is no description suggesting that the specific thiazole ring-containing structure disclosed in the present invention is necessary for improving the property as the organic semiconductor material.
Patent Document 1: Japanese Patent Publication Open to Public Inspection (hereafter referred to as JP-A) No. 5-55568
Patent Document 2: JP-A 5-190877
Patent Document 3: JP-A 8-264805
Patent Document 4: JP-A 2003-119255
Patent Document 5: JP-A 2004-282039
Non-patent Document 1: “Science” vol. 289, p. 599, 2000
Non-patent Document 2: “Nature” vol. 403, p. 521, 2000
Non-patent Document 3: “Advanced Material” No. 2, P. 99, 2002